Injection of a low dose of haloperidol, that has no obvious behavioral effects in normal mice, produces akinesia, catalepsy, and sensory neglect in MPTP-treated mice. GM1 ganglioside treatment eliminates all of these behavioral impairments and also partially restores striatal dopamine content. These observations suggest that the MPTP-treated mouse may be a valuable model for studying mechanisms underlying parkinsonism and that administration of GM1 ganglioside may be an effective therapy.